Terminals may be generally classified as mobile/portable terminals or stationary terminals according to their mobility. Mobile terminals may also be classified as handheld terminals or vehicle mounted terminals according to whether or not a user can directly carry the terminal.
Functions of mobile terminals are diversified. These functions include, for example, data and voice communication, photographing and video shooting through a camera, voice recording, music file playback through a speaker system, and outputting an image or video to a display unit. Some terminals are equipped with an electronic gaming function or multimedia player function. In particular, recently released mobile terminals are capable of receiving multicast signals for providing visual content, such as broadcast and video or television programs. In order to perform such functions, the mobile terminals may be basically connected to other devices or networks using various communication protocols, and provide ubiquitous computing to the user. That is, mobile terminals have evolved into smart devices that enable connectivity to a network and ubiquitous computing.
In recent years, as smart devices are increasingly used to play games and watch images, there are attempts to implement virtual reality on smart devices in order to provide users with a better experience. Virtual reality is based on stereoscopic images provided to users. Most smart devices are basically not designed to realize stereoscopic images. Therefore, in order to view stereoscopic images, separate software or hardware such as a dedicated application for realizing a stereoscopic image is required. In addition, even if a smart device is capable of realizing a complete stereoscopic image without any separate software or hardware, a separate extension device is required in order to allow a user to sufficiently enjoy stereoscopic images using a display of the smart device, which is relatively small. Recently, auxiliary devices capable of sufficiently providing a user with virtual reality, that is, a stereoscopic image enlarged to a sufficient size by using the display of a smart device have been developed according to the need. In particular, considering user convenience, these auxiliary devices are mostly designed to be mounted directly on the user's head, and the smart device may be mounted in the auxiliary devices to substantially provide virtual reality.
Unlike general virtual-reality-based functions such as watching movies or normal application execution, some functions, such as gaming may be performed as intended only when dynamic motion of a user is tracked. In order to optimally provide virtual reality regarding such functions, the head motion of the user reflecting change in the user's gaze needs to be tracked. Thus, since the smart device is worn on the user's head by the auxiliary device, motion of the head may be tracked by tracking the motion of the smart device. However, while smart devices are capable of providing most of the functionality required for virtual reality, they may not completely track their own motion (i.e., head motion) due to the limited functionality of the sensor.
Therefore, along with the above-mentioned auxiliary device, the smart device needs to be further improved so as to actually track motion thereof, that is, the head motion of the user, in order to optimally perform the virtual-reality-based function. In addition, a method for optimally controlling the improved smart device is required in order to perform the function of tracking the head motion, and further to improve the related user experience.